Page 104 - General Knowledge

GENERAL KNOWLEDGE 2019

 There are two important layers in the ionosphere viz. E layer or Kennelly Heavy side layer
that reflects the medium radio waves, thus helping in short distance radio communication
and F layer or Appleton layer that reflects the short radio waves and helps in long distance
radio communication.
 The outermost layer of the Earth‘s atmosphere is known as the Exosphere. It is so highly
rarefied a region that its boundary is not clear.
Lithosphere
 The lithosphere is an Earth‘s outermost layer, composed of rocks in the crust and upper
mantle that behave as brittle solids.
 The rigid lithosphere sits on the top of the asthenosphere, a layer of the mantle in which
rocks are hot and deformable.
 The lithosphere is the solid, rocky crust covering the entire planet. This crust is inorganic and

is composed of minerals.
 It covers the entire surface of the earth from the top of Mount Everest to the bottom of the
Mariana Trench.
 The actual thickness of the lithosphere varies considerably, and can range from roughly 40
km to 280 km.
 Earth‘s lithosphere includes the crust and the uppermost mantle, which constitute the hard
and rigid outer layer of the Earth.
 The lithosphere is subdivided into tectonic plates.
 The lithosphere ends at the point when the minerals in the earth‘s crust begin to
demonstrate viscosity and fluid behaviors.
Rocks
 The earth‘s crust is formed of mineral materials called rocks.
 The rocks which form the substructure of our lithosphere are grouped into three broad
categories:

Igneous Rocks
 Igneous rocks are formed by the solidification of molten magma from the interior of the earth.
 About 95% of the earth‘s crust is made of this type of rock. In fact, all other types of rocks
originate from these rocks, and therefore, they are also called primary rocks.
 Igneous rocks are of three types.

Characteristics of Igneous Rocks

 The igneous rock does not contain layers.
 They are without fossils and the upper part of the rock contains joints.
 They are formed by volcanic lava.
 They are crystalline rocks and impervious rocks.
 They are massive and the weathering effect is difficult over them.
 They are primary rocks of the crust, hence are also called the primary rocks.

Sedimentary Rocks
 These rocks are formed from the sediment deposits on the ocean beds.
 They comprise only about 5% of the earth‘s crust, but cover about 75% of the total land
surface.

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